The invention relates to a device for exchanging a die plate of a prilling tower, wherein molten bisphenol A is introduced into the prilling tower through a plurality of dies located in the die plate and is cooled to room temperature with a view to the production of prills, and also to a process for automated exchange by means of such a device.
Bisphenols are chemical compounds with two phenol groups, obtained by causing phenol to react with ketones, whereby bisphenol A (2,2-bis(4-hydroxyphenyl)propane) is formed as a result of the reaction of phenol and acetone. Bisphenol A is processed further into epoxy resins, polycarbonates and polysulfones. With a view to facilitating filling, transport and storage, granular material, flakes or prills are produced from a bisphenol melt by cooling, whereby prills present advantages over granular material or flakes by reason of their lower proportion of dust and better flow properties.
A process for producing bisphenol A prills is known from JP-6-107 581, wherein molten bisphenol A is charged in the top region of a prilling tower and cooling gas, which abstracts the heat of fusion from the falling droplets of melt, is introduced in counter-flow at the bottom of the prilling tower. The solidified prills are removed at the bottom of the prilling tower.
Charging of the bisphenol melt in the top of the prilling tower is effected in this case by means of a die plate which is arranged on the top of the prilling tower. With a view to uniform distribution of the bisphenol melt, the die plate is preferably spherically domed. In the die plate a plurality of bores is uniformly distributed on the surface of the die plate.
The object underlying the invention is therefore to create a device for exchanging such a die plate that enables the initial pressure of the die plate to be maintained within a defined range for variable load ranges of a prilling tower. Moreover, it is desirable that the die-exchanging device can be operated automatically from outside and causes no unnecessary stoppage times of the prilling tower in the event of a change of the load range.
With regard to the device, the object is achieved in that at least two die plates are provided that are capable of being brought in linear manner along a guide into an operating position or an exchange position by means of a suitable drive mechanism. As regards the process, the object is achieved by virtue of the following steps:
redirection of the bisphenol melt from the prilling tower into the melt container,
feeding of nitrogen into the prilling tower over a predetermined period,
relaxation of the pressure in the prilling tower,
release of the contact pressure on the die plate,
actuation of the displacement cylinder with a view to displacing a die plate from the exchange position into the operating position,
application of contact pressure onto the die plate,
feeding of nitrogen into the prilling tower over a predetermined period and
redirection of the bisphenol melt from the melt container into the prilling tower.